1. Field of the Invention
The present invention pertains to the novel application of a particular circulation technique to an existing drilling method. The drilling method is percussion drilling with the hammer outside the hole. The circulation technique is double tube reverse circulation. This technique has already been used in drillings, but heretofore only in totally different fields, for instance, in tricone drilling.
2. Description of the Relevant Art
Soil drilling by means of a cutter screwed onto the lower extremity of a tube whose top end is subjected simultaneously to percussion and rotation transmitted through a suface hammer, has been known for a long time.
As drilling progresses, tubular elements are screwed on the top end of the tube, which tubular elements are again subjected to the action of the drilling mechanism. The tube is used to inject a fluid such as air or water. The role of the fluid is to clean the cutter, free the rock debris from the bottom of the hole and bring it back up to the surface via the annular space created between the tube and the ground.
This method presents two main disadvantages. First, the fluid loaded with the excavational debris can be contaminated by other debris torn away from the wall during raising, preventing the reconstruction of the successive layers penetrated. Second, the collars used to assemble together the tubular elements protruding into the drill-hole contribute to the degradation of the wall and create a permanent risk of jamming.
The aim of the present invention is to circumvent these disadvantages and to achieve drill-holes of better quality, as well as to make "drilling with hammer outside the hole" an actual tool of geological exploration by producing a good sampling of the layers penetrated. It is a further aim to achieve these goals at a lesser cost than conventional core-sampling.